The present invention relates to systems and methods for spinal surgery. More particularly, the present invention relates to systems and methods for detecting fracture in vertebrae during the insertion and setting of a pedicle screw.
In the treatment of spinal conditions caused by abnormal motion of the vertebrae, it is often desirable to combine two or more vertebrae in the thoracic, lumbar, or transperitoneal portion of the spine. Spinal fusion is one such surgical procedure by which two or more vertebrae are fused together with the aid of screws through the pedicles of affected vertebrae. According to this procedure, the location for a screw opening is first identified in the pedicle of a vertebra. A pilot hole is then formed at each opening with a probe or a drill. Once the pilot holes are formed, a screw is driven into each pilot hole by a suitable instrument. This process is generally repeated for an adjacent vertebra. Metal rods are then secured to adjacent pedicle screws on corresponding sides of the vertebrae to effectively “fuse” adjacent vertebra together.
Proper placement of a pedicle screw according to this procedure is shown in FIGS. 1A-B. When a pedicle screw 10 is properly aligned within the pedicle portion 12 of the vertebra 14, the threaded portion of the screw 10 is disposed entirely within the vertebra 10. If a pedicle screw 10 is improperly aligned, however, the pedicle 12 can become breached, cracked, or otherwise compromised. Potentially, the threaded portion of the screw 10 can breach the vertebra cortex 16 and impinge adjacent nerves. As a result, various attempts have been undertaken to detect fracture in a pedicle portion of a vertebra. One method involves the application of an electric potential to the pilot hole during its formation in the pedicle. According to this method, a lead wire is placed within the pilot hole, or to the pedicle screw once it is placed, and an impulse current is applied to the lead wire. If the pedicle is breached, one or more muscle groups can contract in response to the impulse current. The contraction can be detected visually or with the aid of one or more recording electrodes. If the pedicle has not been breached, the pedicle effectively insulates the impulse current, preventing a contraction of the patient's muscle groups.
There are a number of problems with the above method. First, recording electrodes, if used, are subject to misapplication and therefore will not accurately indicate a breach in the pedicle. Second, the L1 vertebra up to and including the T6 vertebra innervate abdominal muscles whose contraction can be difficult to monitor, particularly for overweight patients. Third, there are no suitable recording sites corresponding to the T6 vertebra up to and including the T2 vertebra.
Therefore, there remains a need for a low-cost system and method for detecting fracture in a pedicle portion of a vertebra at all levels. In particular, there remains a need for an improved system and method for detecting fracture of a pedicle portion of a vertebra during application of a pedicle screw while offering greater accuracy over conventional methods of fracture detection.